The performance of wireless communication systems can be greatly enhanced by utilizing antenna diversity or smart antennas. Such antenna systems make use of multiple antennas and they have been incorporated into the base stations of most mobile telephone systems in use today.
Adoption of diversity or smart antennas in compact wireless communication handsets however has not been widespread, although several investigations have been reported. Possible explanations for this are that the volume of dual or multiple antennas is currently too large for modern compact handsets and that the improved performance of the handset does not sufficiently compensate for increases in receiver complexity.
Some of these issues are being addressed and recently developed antenna algorithms such as BLAST (Bell laboratories layered space-time) may overcome the complexity verses performance issue (G. J. Foschini, “Layered Space-Time Architecture for Wireless Communication in a Fading Environment when Using Multi-Element Antennas”, Bell Labs Technical Journal, Vol 1, No.2, Autumn 1996, pp.41-59). However the antenna volume that dual or multiple antennas occupy remains a problem. In previous work significant reductions in antenna size have been achieved for individual antennas (see for example the following documents, the disclosure of which is incorporated herein by reference: M. T. K. Tam and R. D. Murch, “Compact Sector and Annular Sector Dielectric Resonator Antennas”, IEEE Transactions on Antennas and Propagation, Vol. 47, No.5, May 1999, pp.837-842; C. R. Rowell and R. D. Murch, “A compact PIFA suitable for dual frequency 900/1800 MHz operation”, IEEE Transactions on Antennas and Propagation, Vol 46, No.4, April 1998, pp.596-598; M. A. Jensen and Y. Rahmat-Samii, “Performance analysis of antennas for hand-held transceivers using FDTD”, IEEE Transactions on Antennas and Propagation, Vol. 42, No.8, August 1994, pp.1106-1113; M. G. Douglas, M. Okoniewski, M. A. Stuchly, “A planar diversity antenna for hand-held PCS devices”, IEEE Transactions on Vehicular Technology, Vol. 47, No.3, August 1998, pp. 747-54; and G. F. Pedersen and J. B. Andersen, “Integrated antennas for hand-held telephones with low absorption”, IEEE Vehicular Technology Conference, June 1994, pp. 1537-1541), however compact diversity antennas have not been well studied. The current approach to achieve antenna diversity at the handset is based on placing two or more individual compact antennas on the handset in positions that provide low envelope cross-correlation coefficients (see the papers by M. A. Jensen et al. and M. G. Douglas et al. mentioned above).
This approach is good but the overall volume the antennas occupy increases directly with their number and becomes too large for compact handsets.